Thank you for reach out to us. We see this issue typically when users either have a proxy setup on their network blocking certain ports or are running any sort of network monitoring programs such as LittleSnitch.
Also, go to your Firewall settings and make sure you have access enabled to InDesign and Flash Player, if they are not found add them to the exception list.
Please look into this and let me know if you are still unable to see the Plugin panels after restarting InDesign.
Mag+ Support Team